High-Availability Seamless Redundancy (Hsr); Daisy Chain - GE 350 Communications Manual

CHAPTER 3: ETHERNET INTERFACE

High-availability Seamless Redundancy (HSR)

Daisy Chain

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350 FEEDER PROTECTION SYSTEM – COMMUNICATIONS GUIDE
HSR defines a redundancy protocol for high availability in substation automation
networks, based on PRP principles, provides the property of zero recovery time, typically
used in ring topology but applicable to any topology.
In the SR350 relay, HSR is implemented in devices with communication option number 5
and it has two fiber optics. A frame is sent over both ports. A destination should receive, in
the fault-free state, two identical frames within a certain time skew, forward the first frame
to the application and discard the second frame when (and if) it comes. A sequence
number is used to recognize such duplicates.
In contrast to PRP (IEC 62439-3- Clause 4), with which it shares the operating principle, HSR
nodes are arranged into a ring, which allows the network to operate without dedicated
switches, since every node is able to forward frames from port to port. HSR originally
meant "High-availability Seamless Ring", but HSR is not limited to a simple ring topology.
Redundant connections to other HSR rings and to PRP networks are possible.
A daisy chain is an interconnection of devices where each device is connected in series to
the next.
When an Ethernet daisy-chain redundancy is selected, the 350 has two Ethernet ports and
it is working as an Ethernet unmanaged switch. The two Ethernet ports are used for
conncting each device to the ports of its two neighboring devices, see figure.
Figure 3-4: Ethernet daisy-chain redundancy
Each device in the daisy chain forwards the message until it reaches the destination.
Ports A and B use the same MAC (physical device) address and operate by chaining one
device with the next one.
It is important not to create a loop in this topology. Both ends of the chain can be
connected to different networks. The device operates only with one IP address through
these two ports.
REDUNDANCY OPTIONS
3–5